Feathering controllable pitch propeller



May 3, 1966 K. E- SCHOENHERR FEATHERING CONTROLLABLE PITCH PROPELLERFiled Dec. 2, 1964 v 4 Sheets-Sheet 2 I KARL 5. SCHOE'NHERR AGEN y 1966K. E. SCHOENHERR 3,249,161

FEATHERING CONTROLLABLE PITCH PROPELLER Filed Dec. 2, 1964 4Sheets-Sheet 3 INVENTOR.

FIG. 5.

y 966 K. E. SCHOENHERR 3,249,161

FEATHERING CONTROLLABLE PITCH PROPELLER Filed Dec. 2, 1964 4Sheets-Sheet 4 INVENTOR. F/ 6 KARL E. SCHOENHERR United States Patent M3,249,161 FEATHERING CONTROLLABLE PITCH PROI'ELLER Karl E. Schoenberr,7653 Western Ave. NW., Washington, D.C. Filed Dec. 2, 1964, Ser. No.415,555 2 Claims. (Cl. 170-16053) The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

The present invention relates to marine propellers and more particularlyto a propeller which will reduce the fluctuations of the propellerforces and thus minimize vibrations.

The propeller located behind the hull of a ship operates in the waterdisturbed by the hull, or the so-called wake of the ship. The velocitydistribution in this wake is not uniform, but in general varies radiallyand circumferentially. Radial variation is not harmful as this can beallowed for in the design of the propeller. However, circumferentialvariation is harmful because this variation produces pressurefluctuations causing the angle of attack of the propeller blade to varyabout a means value as the blade goes through one complete revolution.Thesepressure fluctuations are radiated into the surrounding water andare transmitted to the hull giving rise to the primary cause ofvibration in the ship structure. Vibrations, in turn, are highlyobjectionable for marine vessels and must be avoided ifpossible.

Heretofore, attempts to reduce vibrations have resulted in arrangementsof resiliently mounted propeller blades and standard controllable pitchpropellers, wherein the pitch of the propellers are adjusted for varyingloads and to reverse thrust without varying the direction ofv rotation'of the shaft. The pitch adjustment, usually being effected by a bellcrank arrangement in the interior of the hub activated by mechanical orhydraulic means. The prior art devices and arrangements have not provensatisfactory for the reduction of vibration due to the fluctuating wakeforces. Y

The general purposes of this invention is to reduce the fluctuations ofthe propeller forces and thus minimize vibrations. To attain this, thepresent invention contemplates a self-adjusting feathering controllablepitch propeller arrangement whereby force fluctuations are reduced andvibrations are minimized.

An object of the present invention is the provision of a self-adjustingfeathering controllable pitch propeller for minimizing ship vibrations.

' Another object is to provide a rotatable blade propeller for efiicientship movement in the rearward direo tion.

' A further object of the invention is the provision of a self-balancingpropeller arrangement wherein an equilibrium of forces and moments ismaintained.

Other objects and advantages of this invention will hereinafter becomemore fully apparent from the following description of the annexeddrawings which illustrate preferred embodiments and wherein:

FIG. 1 is a representative section of a propeller blade showing theforces acting upon it;

FIG. 2 is a longitudinal sectional view along the lateral plane of aship of a two-bladed propeller embodiment constructed according to thepresent invention;

FIG. 3 is a transverse view of the propeller of FIG. 2 projected on aplane transverse to the fore and aft axis of the ship;

FIG. 4 is a top view of a propeller of FIG. 3 showing the self-balancingfeature of the present invention;

3,249,161 Patented May 3, 1966 FIG. 5 is a transverse sectional view ofa four-bladed propeller constructed according to the present inventionshowing the interior hub connections;

FIG. 6 is a transverse sectional view of a further embodiment of thepresent invention wherein resilient means control blade adjustments; and

FIG. 7 is av view of the resilient means of FIG. 6'.

FIG. 1 discloses the action of a standard screw propeller with respectto a tri-rectangular system of coordinates wherein OY is the axis aboutwhich the propeller turns and along which it advances and OZ is the axisnormal to the plane of the drawings. An ogive 11 represents a bladesection at radius R from the center of the hub, having a lineartangential velocity of wR and velocity of advance of the propeller beingVa. From propeller theory it is then known that the resultant velocity Wrelative to the blade section is given by the expression:

u is the rotational slip velocity v is the axial slip velocity.

The propeller is usually so designed that W meets the face of the bladesection at an angle a, the so-called hydrodynamic angle of attack. Thisangle of attack causes a lift force L to be produced, the magnitude ofwhich may be expressed by the equation:

p is the density of the medium A is the area of the blade W is theresultant velocity flu) is some function of a.

From this equation it is seen that when 0: increases, L increases andvice versa. For a given propeller, the angle of attack it varies wheneither the vector Va, the vector (wR), or the ship velocity vectors uand v change. When the propeller is working behind a ship in thesocalled wake of the ship, the wake which is not a uniform current but ahighly irregular one causes the angle of attack a to vary about a meanvalue as the blade goes through one complete revolution. Therefore, thewake cause the angle a to vary and in turn causes the lift force L andthe components of this force to fluctuate. These force fluctuations arethe primary cause of vibrations in the ship structure.

The present invention minimizes force fluctuations caused by variableinflow into the propeller (variable wake) by feathering the propeller,that is, by reducing the angle of attack a when Va, the velocity ofadvance of the propeller, tends to decrease (region of high wake), andincreasing a when Va tends to increase (region of low wake). Since theangle of attack is usually on the order of four to six degrees, angularadjustments (Au) required to smooth out these fluctuations neednot begreater than about plus or minus 2. To accomplish angular adjustments,each blade must of course be rotatable about the OZ axis as shown inFIG. 2. Control of the adjustments can be effected in sever-a1 ways; (a)through a bell crank arrangement inside the hub actuated by mechanicalor hydraulic means and programmed in suitable manner (b) throughresilient means inside the hub or (0) through a special design of theblades and of the blade mounting on the hub as hereinafter described.

this embodiment the multiple-bladed propeller has an evennumber ofblades, that is two, four, six blades.

FIG. 2 is the longitudinal view of the propeller, that is,

the propeller projected on the lateral plane of the ship. FIG. 3 is thetransverse view, that is the propeller projected on a plane transverseto the fore and aft axis of the ship.

FIG. 2 shows in section the interior hub connections of the two-bladedpropeller 13. The drive shaft is connected to the hub 17 at one end bysuitable mountings shownas a ring 19 and a plurality of bolts 21 and ahub cap or fairwater 23 is placed over a cover plate 25 at the otherend. The two-bladed propeller having an upper blade 27 and a lower blade29 is connected together in the hollow, central portion of the hub 17.Each blade is secured by any suitable means to a blade spindle 31 whichextends into the center of the hub. The blade spindles are connectedtogether by any suitable means shown as a sleeve 33 having two pins 35,one pin extending through the end portion of each spindle and throughthe sleeve. The sleeve thereby forms a rigidly connected two-bladepropeller and the spindles ride on bearings 37 which are provided aboutthe blade spindles, thereby enabling the rigidly connected two-bladedpropeller 13 a to rotate about the OZ axis. The rigidly connectedtwobladed propeller construction causes the rotational mo tion of eachpair of blades to be such that when the angle of attack or increases forthe top blade by an amount Au it decreases for the bottom blade by thesame amount.

The novel arrangement of FIG. 2 is self balancing in ahead operation asis shown in connection with FIG. 4. In this figure the OZ axis is normalto the plane of the drawing, the direction of rotation of the shaft isshown and the blade area is skewed aft as shown in FIG. 3 wherein thecenter of pressure P of the blade 27 lies rear ward of the OZ axis. Whenthe ship velocity (Vs), the velocity of advance (Va), and the rotationvelocity (wr) are all uniform, the lift forces L and and L1 are equal.Since that the opposing blades 27 and 29 have the same shape, themoments of these forces about the OZ axis are also equal; that is M themoment L=lift force X=distance from the OZ axis to the pressure point oneach blade When there is some irregularity in the wake, the inflow angleof the upper blade is increased by the amount Act but not for the lowerblade, then the force L increases; this causes an inequality in moments,that is And the systemrotates about OZ in a clockwise direction. Thisrotation tends to diminish a for the upper blade 27 and tends toincrease it for the lower blade 27. The tendency therefore is to restoreequilibrium in moments. Hence, there is a feathering action by theblades which tends to counteract the force of fluctuations reduced bywake or other flow regularities. The blades therefore exhibit anoscillatory motion in a variable wake, oscillating plus or minus twodegrees about a mean value. In prior systems, the different pressures onthe blades would be transmitted to the hub and the surrounding water dueto the rigid connections of the hub and blade.

The system described is in stable equilibrium only for normal aheadoperations. When the ship is backing, the equilibrium is unstablebecause the propeller is designed for forward operation. This inventionprovides suflicient room so that the blades can turn through 180 degreesso that, when the ship is backing and the blades have turned through the180 degrees, operation is the same as for normal ahead operations. Thisreversal feature of the blades for backing operation is very usefulbecause blade sections designed for best efliciency for ahead operationbecomes very ineflicient forbacking. As a result of this decreasedefiieiency, the propulsive eificiency of a ship when back ing is no morethan /3 of the propulsive efiiciency when moving forward. Therefore, thenew propeller not only tends to smooth out force fluctuations'but isalso capable of improving the efficiency astern by as much as percentwhich permits reducing the size of the astern turbine without imparingmaneuverability.

FIG. 5 is an embodiment of a four-bladed propeller 39 constructedaccording to the present invention. One pair of blades 27 and 2f areconnected together by a straight connecting rod .41 attached to therespective spindles 31 and a second pair of blades and 43 are connectedtogether by a forked connecting rod 47 with the straight connecting rodinserted through the fork. Mechanical limit stops 49 are provided aboutthe blade to allow a rotation of the blade of approximately plus orminus 5 degrees, thereby insuring adequate rotational movement of theconnecting rods Without interference.

A second way to smooth out wake irregularities which may be used on apropeller having any number of blades, is to control the angle ofincidence of the blade by resilient means. This embodiment is shown inFIGS. 6 and 7 wherein the same reference numerals are employed as inthe, previous figures. The hub 17 of the multi-bladed propeller 51 has acover, plate 25a mounted on one end and a hub cap or fairwater 23amounted over the cover plate. A plurality of holes 53, equal to thenumber of blades on the propeller are provided in the cover plate 25a.One part 54 of the hole in communicating relationship with the interiorof the hub 17 is square in transverse cross-section and the otherportion 55 of the hole in communicating relationship With the interiorof the fairwater 23a is circular in cross-section with a diametergreater than the greatest dimension of the square hole and abuts thesquare hole at a shoulder 56.. The circular hole and the shoulder form aseat for a resilient element such as a spring which rides on tension rod59 having a middle portion 6%) which is square in cross-section and issupported in sliding contact by the square, hole 54. The spring 57 isadjustably biased against the seat by a tension nut 61 located at oneend of the tension rod 59. The other end of the tension rod is providedwith a cutaway portion which has a longitudinal flat portion 63 abuttinga shoulder 64. A flat, longitudinal flexible band 65 is placed upon'thefiat portion of the rod and'is secured thereto by a clamp and screw 67.The other end portion of the tension band is secured to the spindle 31by any suitable means such as a clamp and screw 69 shown in the drawing.A longitudinal bar 71 having a plurality of apertures 73 at one end issecuredat its other end to cover plate 25a, by a plurality of screws 75.The apertures provide a bearing surface for the. lower part 77 of thespindle 31 which is received by the aperture and is supported thereby.Mechanical stops may also be provided about the blade to limit rotationof the blade.

The operation of the spring biased propeller is essentially as follows.The spring 57 is selected to bias the propeller blades to apredetermined pitch for a desired flow condition. When the propellerrevolves about its axis, the pressure on the blades due to the wakecauses the spring 57 to be compressed and the tension bands 65 to wraparound the spindle 31 until the compression force on the spring andrestoration force of the spring is in equilibrium and the predeterminedpitch of the propeller is attained. When the propeller operates inavariable wake, the varying lifting forces on the blade 27 causepredetermined position, which it 'does when the excess pressure isremoved from the blade. The returning of the spring 57 causes thetension band 65 to unwind and in turn the spindle and blade are returnedto the desired operating pitch for the propeller. This spring biasingfeature thus allows a propeller having any number of blades to befabricated for operation according to the principles of the presentinvention.

As discussed before, another way to smooth out wake irregularities inaddition to the aforedescribed passive systems is to alter the angle ofincidence by a programmed mechanical force. Once the wake variation isknown from model tests, the angle of incidence of each blade can becontrolled as the propeller rotates through 360 degrees. By propersequencing of the actuators, which could be hydraulic rams, theoperation of the system can be made automatic. The advantage ofcontrolled adjustment of the angle of incidence over the self-balancingsystem is that wake variations can be anticipated and thereby, forcefluctuations can be completely smoothed out. Another advantage is thatas in the spring biased system, an odd number of blades as well as aneven number of blades, can be used.

Obviously many modifications and variation of the present invention arepossible in the light of the above teachings. It is therefore .to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A feathering controllable pitch propeller for reducing shipvibrations comprising:

a hub;

a plurality of blade spindle-s spaced about said hub, each of saidspindles rotatable in said hub about an axis perpendicular to the axisof rotation of the propeller;

a plurality of propeller blades each of said blades being secured to oneof said blade spindles;

each of said blades having a blade area which is skewed aft and having acenter of pressure lying aft of the blade axis of rotation;

resilient means biasing each of said blade spindles for controlling theangle of attack of the propeller blades in response to wake forcefluctuations;

a cover plate mounted on one end of the hub having a plurality ofcircumferentially spaced apertures;

a tension rod sl-idably mounted in each of the apertures of said coverplate;

a spring mounted in overlying relation to one end of each of said-rods;

holding means forcing each of said springs against one side of saidcover plate;

a plurality of flexible tension bands each having one end secured to theother end of one of said rods and having its other end secured to one ofsaid spindles;

whereby said band winds around said spindle in response to an increasein pressure on the associated blade and unwinds under the force of saidspring in response to a decrease in pressure;

each of said apertures in said cover plate comprising two portions, withone of said portions being square in transverse cross-section, saidsquare portion receiving a square middle portion of said tension rodthereby preventing rotational movement of said rod and twisting of saidband;

said other portion being circular in transverse crosssection and havinga diameter greater than the greatest dimension of the square portion,whereby said circular portion forms a seat for said spring; and

a longitudinal bar secured at one end to said cover plate, said barhaving aperture means therein re- 6 ceiving a portion of said bladespindles for providing bearing surfaces for said blade spindles.

2. A feathering controllable pitch propeller tor reducing shipvibrations comprising;

a hub;

a plurality of blade spindles spaced about said hub, each of saidspindles rotatable in said hub about an axis perpendicular to the axisof rotation of the 'propeller;

a plurality of propeller blades each of said blades being secured to oneof said blade spindles;

each of said blades having a blade area which is skewed afit and havinga center of pressure lying aft of the blade axis of rotation;

a plurality of resilient means, each of said resilient means biasing oneof said blade spindles for independently controlling the angle of attackof the associated propeller blade in response to wake force fluctuationsWithout afiecting the angle of attack of the other propeller blades;

a cover plate mounted on one end of the hub and having a plurality ofcir-cumferentially spaced apertures;

a tension rod slidably mounted in each of the apertures of said coverplate;

said resilient means comprising a spring mounted in overlying relationto one end of each of said rods;

holding means on said one end of each rod, said holding means forcingeach of said springs against one side of said cover plate;

a plurality of flexible tension bands each having one end secured to theother end of one of said rods and having its other end secured to one ofsaid spindles, whereby said band winds around said spindle in responseto an increase in pressure on the associated blade and unwinds under theforce of said spring in response to a decrease in pressure;

each of said apertures in said cover plate comprising two portions, afirst portion receiving a portion of said tension rod and cooperatingthere-with for preventing rotational movement of said rod and twistingof said band;

the second portion of each aperture being circular in transverse.crosssection and having a diameter greater than the greatest dimensionof said first portion, whereby said circular portion forms a seat forsaid spring; and

- a longitudinal bar secured at one end to said cover plate, said barhaving aperture means therein receiving a portion of said blade spindlesfor providing bearing surfaces for said blade spindles.

References Cited by the Examiner UNITED STATES PATENTS 608,265 8/1898Olsen 160.1 1,841,497 1/1932 Parham 170--160.51 1,919,586 7/1933 Dodge170-16051 2,231,464 2/1941 Dubbs 170160.57 2,395,862 3/1946 Freeman etal. 170l60.51 X 2,483,913 10/1949 Lampton 170--160.52 2,583,369 1/1952Fumagalli .170-13 X FOREIGN PATENTS 563,529 9/1923 France.

888,497 9/ 1943 France.

SAMUEL LEVINE, Primary Examiner.

JULIUS E. WEST, Examiner.

E. A. POWELL, JR., Assistant Examiner.

1. A FEATHERING CONTROLLABLE PITCH PROPELLER FOR REDUCING SHIPVIBRATIONS COMPRISING: A HUB; A PLURALITY OF BLADE SPINDLES SPACED ABOUTSAID HUB, EACH OF SAID SPINDLES ROTATABLE IN SAID HUB ABOUT AN AXISPERPENDICULAR TO THE AXIS OF ROTATION OF THE PEROPELLER; A PLURALITY OFPROPELLER BLADES EACH OF SAID BLADES BEING SECURED TO ONE OF SAID BLADESPINDLES; EACH OF SAID BLADES HAVING A BLADE AREA WHICH IS SKEWED AFTAND HGAVING A CENTER OF PRESSURE LYING AFT OF THE BLADE AXIS OFROTATION; RESILIENT MEANS BIASING EACH OF SAID BLADE SPINDLES FORCONTROLLING THE ANGLE OF ATTACK OF THE PROPELLER BLADES IN RESPONSE TOWAKE FORCE FLUCTUATIONS; A COVER PLATE MOUNTED ON ONE END OF THE HUBHAVING A PLURALITY OF CIRCUMFERENTIALLY SPACED APERTURES; A TENSION RODSLIDABLY MOUNTED IN EACH OF THE APERTURES; OF SAID COVER PLATE; A SPRINGMOUNTED IN OVERLYING RELATION TO ONE END OF EACH OF SAID RODS; HOLDINGMEANS FORCING EACH OF SAID SPRINGS AGAINST ONE SIDE OF SAID COVER PLATE;A PLURALITY OF FLEXIBLE BANDS EACH HAVING ONE END SECURED TO THE OTHEREND OF ONE OF SAID RODS AND HAVING ITS OTHER END SECURED TO ONE OF SAIDSPINDLES; WHEREBY SAID BAND WINDS AROUND SAID SPINDLE IN RESPONSE TO ANINCREASE IN PRESSURE ON THE ASSOCIATED BLADE AND UNWINDS UNDER THE FORCEOF SAID SPRING IN RESPONSE TO A DECREASE IN PRESSURE; EACH OF SAIDAPERTURES IN SAID COVER PLATE COMPRISING TWO PORTIONS, WITH ONE OF SAIDPORTIONS BEING SQUARE IN TRANSVERSE CROSS-SECTION, SAID SQUARE PORTIONRECEIVING A SQUARE MIDDLE PORTION OF SAID TENSION ROD THEREBY PREVENTINGROTATIONAL MOVEMENT OF SAID ROD AND TWISTING OF SAID BAND; SAID OTHERPORTION BEING CIRCULAR IN TRANSVERSE CROSSSECTION AND HAVING A DIAMETERGREATER THAN THE GREATEST DIMENSION OF THE SQUARE PORTION, WHEREBY SAIDCIRCULAR PORTION FORMS A SEAT FOR SAID SPRING; AND A LONGITUDINAL BARSECURED AT ONE END TO SAID COVER PLATE, SAID BAR HAVING APERTURE MEANSTHEREIN RECEIVING A PORTION OF SAID BLADE SPINDLES FOR PROVIDING BEARINGSURFACES FOR SAID BLADE SPINDLES.